Civilization V - technological abomination. To avoid getting into details, a game that launched with a build that was marked Release and should've been marked Early Alpha. Disturbingly awesome potential within the game.
Worms: Reloaded - any 3D is an abomination of Worms that I'm gonna file along with it (and as much worse than it), but for what was supposed to be a simple rebuild of a game that old and simple without anything too fancy added, they still managed to make it much worse than either Armageddon or WWP (mainly the lack of options within the game setups and a worsened UI).
GTA IV - I like it, but it's still the black sheep of the family compared to the others. Some fantastic additions, but it doesn't change the fact it traded the soul of the franchise for them or that it's... I won't say worse, but a lot less better than others on the whole.
CoD: Black Ops - not talking multiplayer, but singleplayer vastly disappointed. Old CoD games were decent fun back in the day, first MW had a fantastic story and brought very polished gameplay (which was in itself an innovation at the time) and great visuals, WaW brought an interestingly depressing FPS (a pretty good one, just depressing in atmosphere), MW2 brought less story for more action and a great co-op/challenge mode and Black Ops... did fuck all.
Dragon Age 2 - need I beat the ashen remains that were once a dead horse? Awakening wasn't great either, boring mostly due to the fact it added next to nothing to a game that had more than enough content to begin with.
Mass Effect - mostly for being a shoddy PC port, though I'm not sure how I'd fare with the whole RPG aspect of it despite me being a big RPG fan, it didn't seem particularly well made
Probably some more. If I have to pick one, it'll be Civilization V. Just thinking of it's potential being ruined by nothing other than lack of work on the game is making me genuinely sad and angry. Polish the game, sort out at least the major issues (optimization, crashes, memory leaks), make the AI work right (some diplomacy options are completely useless, always being a no even on lower difficulties and I won't even talk about their move back/front/back/front combat abilities) and you've got yourself not just a decent, but one of the best games of the decade. Instead, last I checked, most of the major issues were still there (almost a year post-release) and the motherfuckers were making DLC upon DLC for extra profits.
'[/quote]